Bit Cone With Hardfaced Nose

ABSTRACT

A drill bit for drilling a wellbore, the drill bit having a cutter which has tungsten carbide inserts and a spear point. The spear point has a neck that joins a smooth portion of the cutter and blades that extend from the neck and converge to an apex. The blades define valleys or spaces between them. A layer of hardfacing is applied to the entire spear point including the interim spaces and the neck.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to provisional application 61/088,991, filled Aug. 14, 2008.

FIELD OF THE INVENTION

This invention relates to improvements to earth-boring bits having rotating cones with cutting structures and in particular to hardfacing a spear point to enhance wear resistance.

BACKGROUND OF THE INVENTION

In drilling bore holes in earthen formations by the rotary method, rock bits fitted with one, two or three rolling cutters are employed. The bit is s secured to the lower end of a drill string that is rotated from the surface, or the bit is rotated by downhole motor or turbines. The cutters mounted on the bit roll and slide upon the bottom of the bore hole as the bit is rotated, thereby engaging and disengaging the formation material to be removed. The roller cutters are provides with cutting elements that are forced to penetrate and gouge the bottom of the borehole by weights of the drill string. The cuttings from the bottom and sidewalls of the borehole are washed away by drilling fluid that is pumped down from the surface through the hollow drill string.

One type of cutting element in widespread use is a tungsten carbide insert which is interference pressed into an aperture in the cutter body. Tungsten carbide is metal which is harder than the steel body of the cutter and has a cylindrical portion and a cutting tip portion. The cutting tip portion is formed in various configurations, such as chisel, hemispherical or conical, depending upon the type of formation to be drilled. Some of the inserts have very aggressive cutting structure designs and carbide grades that allow the bits to drill in both soft and medium formations with the same bit.

Another type of rolling cutter earth-boring bit is commonly known as a “steel-tooth” or “milled-tooth” bit. Typically these bits are for penetration into relatively soft geological formations of the earth. The strength and fracture-toughness of the steel teeth permits the use of relatively long teeth, which enables the aggressive gouging and scraping actions that are advantageous for rapid penetration of soft formations with low compressive strengths.

However, it is rare that geological formations consist entirely of soft material with low compressive strength. Often, there are streaks of hard, abrasive materials that a steel-tooth bit should penetrate economically without damage to the bit. Although steel teeth possess good strength, abrasion resistance is inadequate to permit continued rapid penetration of hard or abrasive streaks. Consequently, it has been common in the arts since at least the 1930s to provide a layer of wear-resistance metallurgical material called “hardfacing” over those portions of the teeth to the severest wear. The hardfacing typically consists of extremely hard particles, such as sintered, cast, or macro-crystalline tungsten carbide, dispersed in a steel matrix. Such hardfacing materials are applied by welding a metallic matrix to the surface to be hardfaced and applying the hard particles to the matrix to form a uniform dispersion of hard particles in the matrix.

Unlike a tungsten carbide insert bit teeth of a steel-tooth bit are not susceptible to stress cracking due to excessive heat. A steel-tooth bit would be able to drill the relatively soft non-abrasive formations mentioned above with case stress cracking on heel rows of insert bits. However, because of the hardness and thickness of adjacent formations, a steel-tooth bit would wear too quickly, thus is not a preferred choice in those areas.

FIG. 1 shows a prior art earth-boring bit 11, having a body 13 with three bit legs 15 depending therefrom. A cone 17 is rotatably mounted to each of the bit legs 15. Each cone 17 is formed of a steel shell or body. Each cone 17 has a plurality of inner row compacts or carbide inserts 19, arranged in at least one inner row. A plurality of outer or heel row compacts 21 are adjacent to a gage surface 23 of each cone 17. It is common for cones 17 to have different numbers of rows. In the embodiment shown, heel row compacts 21 are generally ovoid, although different shapes could be used.

SUMMARY OF THE INVENTION

In this invention, the bit has a cutter which has tungsten carbide inserts and a spear point. The spear point has a neck that joins a smooth portion of the cutter and blades that extend from the neck and converge to an apex. The blades define valleys or spaces between them.

A layer of hardfacing is applied to the entire spear point including the interim spaces and the neck. This hardfacing may be of a conventional type comprising tungsten carbide particles in a steel alloy matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of a prior art earth-boring bit.

FIG. 2 is a bottom view of an earth-boring bit having a cone hardfaced in accordance with this invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 2, bit 27 of this invention has a body, bit legs, and a threaded section that are not shown but may be the same as in prior art bit 11 of FIG. 1. Bit 27 has a first cone 29, a second cone 31, and a third cone 33. Each cone 29, 31, 33 has a plurality of compacts 35 located on outer and inner rows. Inserts 37 are also located along the inner and outer rows of each cone 29, 31, 33. Compacts 35 are formed of cemented carbide, typically tungsten carbide that is usually homogenous and formed in a die and consolidated by sintering techniques. Optionally, at least one layer of diamond may be formed on the cutting tip. Also, as another option, portions of the carbide material placed in the die and sintered may be of different grades.

First cone 29 has an outer row 39 and an intermediate row 41 of compacts 35, which are located adjacent the gage surface of first cone 29. An inner row 43 is located a short distance inward from intermediate row 41 toward the bit axis. A thin annular conical band 45 is located between intermediate row 41 and inner row 43. First cone 29 has a spear point 47 that is conventional and comprises radially extending blades. A layer of hardfacing 49 is applied over spear 47 and a segment of a nose section 50 of cone 29. A conical surface 51 extends from inner row 43 to the neck portion of spear point 47. A layer of hardfacing 49 may be applied to a portion of conical surface 51 near the neck portion of spear 47. The hardfacing 49 of spear 47 reduces the amount of wear in the nose area 50. Hardfacing 49, combined with the use of compacts 35 on inner row 43, intermediate row 41, and outer rows 39 reduces the total amount of wear of cone 29.

Second cone 31 has an outer row 53 and an intermediate row 55 of compacts 35. The nose portion 56 of cone 31 extends axially from intermediate row 55, forming conical band 57. In this embodiment, an inner row 59 of compacts 35 are located on the nose portion 56 of cone 31. Alternatively, milled steel teeth could be formed on the nose portion 56 of cone 31, in place of compacts 35 on inner row 59. If an inner row of steel teeth were formed on the nose portion 56 of cone 31, hardfacing could be applied over the teeth and sections of the nose portion 56 of cone 31 and conical band 57.

Third cone 33 has an outer row 61 and an intermediate row 63 of compacts 35. The nose portion of cone 33 extends axially from intermediate row 63, forming conical band 65. In this embodiment an inner row 67 of compacts 35 are located on the nose portion of cone 33. An additional set of small compacts 68 are located on the end 69 of the nose portion of cone 33. Alternatively, milled steel teeth could be formed on the nose portion of cone 33, in place of compacts 35 on inner row 67 and compacts 68 on nose end 69. If an inner row of steel teeth were placed on the nose portion of cone 33, hardfacing could be applied over the teeth, and sections of the nose portion of cone 33 and conical band 65.

In operation, bit 27 is run conventionally. The combination of compacts 35, inserts 37, and hardfacing 49 applied to the nose section 50 of cone 29 reduces wear and erosion, increasing the life of the bit 27. While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention. 

1. An earth boring bit, comprising in combination: a body with a longitudinal bit axis; three bit legs depending from the body; first, second, and third cutters, each rotatably mounted to one of the bit legs; at least one of the cutters having a metal shell with a nose section extending inward toward the bit axis from the metal shell, the nose section having compacts located thereon and protruding therefrom for disintegrating an earth formation, the nose section being free of hardfacing; and at least one other of the cutters having a metal shell with a nose section extending toward the bit axis, the nose section of the at least one other of the cutters having hardfacing located thereon.
 2. The earth boring bit of claim 1, wherein the nose section having hardfacing located thereon further comprises: a spear point having a neck which joins the metal shell of the at least one other of the cutters, the spear point having a plurality of blades extending from the neck, the blades converging to an apex and being circumferentially separated from each other about a cutter axis of the at least one other of the cutters, defining a space between each of the blades; and a layer of hardfacing formed on the neck, the blades and the spaces between each of the blades, the hardfacing being tungsten carbide particles in a matrix for protecting the neck and spaces from erosion.
 3. The earth boring bit of claim 1, wherein the nose section having hardfacing located thereon extends a desired distance toward the bit axis and is positioned closest to the bit axis than any of the other cutters:
 4. An earth boring bit, comprising in combination: a body with a bit axis; three bit legs depending from the body; first, second, and third cutters, each rotatably mounted to one of the bit legs; the first cutter having a metal shell with at least one row of compacts located thereon and protruding from the metal shell for disintegrating an earth formation, the metal shell having a smooth conical surface extending inward from the at least one row of compacts, the smooth conical surface being free of hardfacing; a spear point having a neck which joins the smooth conical surface of the first cutter, the spear point having a plurality of blades extending from the neck, the blades converging to an apex and being circumferentially separated from each other about a cutter axis of the first cutter, defining a space between each of the blades; and a layer of hardfacing formed on the neck, the blades and the spaces between each of the blades, the hardfacing being tungsten carbide particles in a matrix for protecting the neck and spaces from erosion.
 5. The earth boring bit of claim 4, wherein the spear point extends axially along the cutter axis of the first cutter a select distance such that the apex of the spear is closer to the bit axis than any portion of the second and third cutters.
 6. The earth boring bit of claim 4, wherein said at least one row of compacts comprises: an outer row of compacts located thereon, an intermediate row of compacts located thereon at a lesser distance from the bit axis than the outer row, and an inner row of compacts located thereon at a lesser distance from the bit axis than the intermediate row.
 7. The earth boring bit of claim 6, wherein the first cutter is free of hardfacing from the outer row of compacts to the neck of the spear point.
 8. The earth boring bit of claim 7, wherein each of the second and third cutters further comprises: a metal shell with a nose section containing at least one compact that protrudes therefrom for disintegrating the earth formation.
 9. The earth boring bit of claim 4, further comprising: the second cutter having a metal shell with a nose section extending axially toward the longitudinal axis from the metal shell along the axis of the second cutter, the nose section of the second cutter having compacts protruding thereform, the nose section of the second cutter being free of hardfacing.
 10. The earth boring bit of claim 9, further comprising: the second cutter having an outer row of compacts protruding therefrom, an intermediate row of compacts protruding thereform and being at a lesser distance from the bit axis than the outer row of compacts of the second cutter and a farther distance from the bit axis than the compacts located on the nose section of the second cutter.
 11. The earth boring bit of claim 4, further comprising: the third cutter having a metal shell with a nose section extending axially toward the longitudinal axis from the metal shell along the axis of the second cutter, the nose section of the third cutter having compacts protruding therefrom, the nose section of the third cutter being free of hardfacing.
 12. The earth boring bit of claim 11, further comprising: the third cutter having an outer row of compacts protruding therefrom, an intermediate row of compacts protruding therefrom and at a lesser distance from the bit axis than the outer row of compacts of the third cutter.
 13. An earth boring bit comprising in combination: a body with a bit axis; three bit legs depending from the body; first, second, and third cutters, each rotatably mounted to one of the bit legs; the first cutter having a metal shell with an outer row, an intermediate row, and an inner row of compacts located thereon and protruding therefrom, the intermediate row being at a lesser distance from the bit axis than the outer row, and the inner row being at a lesser distance from the bit axis than the intermediate row, the metal shell having a smooth conical surface extending inward from the inner row of compacts, the smooth conical surface being free of hardfacing; a spear point having a neck which joins the smooth conical surface of the first cutter, the spear point having a plurality of blades extending from the neck, the blades converging to an apex and being circumferentially separated from each other about a first cutter axis of the first cutter, defining a space between each of the blades; a layer of hardfacing formed on the neck, the blades and the spaces between each of the blades, the hardfacing being tungsten carbide particles in a matrix for protecting the neck and spaces from erosion; and the second and third cutters each having a metal shell with at least one row of compacts located thereon and protruding therefrom.
 14. The earth boring bit of claim 13, wherein the metal shell of the first cutter is free of hardfacing between the outer row and the neck of the spear point.
 15. The earth boring bit of claim 13, wherein the second cutter further comprises: a metal shell with a nose section extending inward toward the bit axis, the nose section of the second cutter having compacts located thereon and protruding therefrom; an outer row of compacts located on the metal shell of the second cutter and protruding therefrom outward from the compacts on the nose section of the second cutter; and an intermediate row of compacts located on the metal shell of the second cutter and protruding therefrom between the compacts on the nose section and the outer row of compacts on the metal shell of the second cutter.
 16. The earth boring bit of claim 15, wherein the third cutter further comprises: a metal shell with a nose section extending inward toward the bit axis, the nose section of the third cutter having a row of compacts located thereon and protruding therefrom; an outer row of compacts located on the metal shell of the third cutter and protruding therefrom; and an intermediate row of compacts located on the metal shell of the third cutter between the compacts on the nose section and the outer row of compacts on the metal shell of the third cutter.
 17. The earth boring bit of claim 16, wherein: a distance between the outer row of compacts and the intermediate row of compacts on the first cutter, measured along the first cutter axis, is less than a distance between the outer row of compacts and the intermediate row of compacts on the second cutter, measured along a second cutter axis.
 18. The earth boring bit of claim 17, wherein: the distance between the outer row of compacts and the intermediate row of compacts on the second cutter is less than a distance between the outer row of compacts and the intermediate row of compacts on the third cutter, measured along a third cutter axis. 